Aluminium carbide formation in interpenetrating graphite/aluminium composites

doi:10.1016/j.msea.2006.11.088

Materials Science and Engineering: A

Volume 448, Issues 1–2, 15 March 2007, Pages 1-6

https://doi.org/10.1016/j.msea.2006.11.088 Get rights and content

Abstract

We have produced interpenetrating graphite/aluminium composites by gas pressure infiltration of aluminium alloys with varying silicon content into porous graphite preforms. Infiltration experiments at 750 °C have shown that a silicon content of up to 18 wt.% can reduce the formation of aluminium carbide but cannot completely deter it. Optical and scanning electron microscopy revealed numerous lath-like interfacial aluminium carbide crystals in the μm regime which, however, did not affect the flexural strength of our composites. Severe aluminium carbide degradation was observed within a few days on composites exposed to ambient conditions. Carbide-free composites were produced by reducing the infiltration temperature to 670 °C for the eutectic alloy.

Introduction

Porous graphite preforms infiltrated with aluminium alloys are attractive materials for lightweight components such as internal combustion engine parts, due to the low thermal expansion, high thermal conductivity and self-lubricating properties of graphite. Such graphite/aluminium (C/Al) composites with an interpenetrating network structure can be produced by infiltration of a porous graphite preform with liquid aluminium alloys.

To achieve a specific mechanical or thermophysical property, the interface between graphite and aluminium is of great importance for the overall performance of composite materials. In particular, chemical reactions at the interface during processing or under service conditions can degrade the thermophysical properties of the composites. The main problems encountered in the development of C/Al composites are non-wetting conditions between the monolithic phases for short contact times, and the reactivity of graphite or carbon with liquid aluminium [1], [2], [3], [4], [5]. At 750 °C, the free energy of formation of Al₄C₃4Al_(l) + 3C_(s) → Al₄C_3(s)is −168 kJ/mol [6]. The undesirable formation of aluminium carbides (Al₄C₃) at the C/Al interface is often observed in graphite/carbon fibre reinforced aluminium matrix composites infiltrated at high temperatures and low cooling rates. In this case, the formation of interfacial Al₄C₃ is accompanied by fibre degradation, and a deterioration of the mechanical properties of the composite is observed [2], [7], [8].

Aluminium carbide crystals are not only brittle, but also highly sensitive to moisture contact and thus promote accelerated fatigue crack growth rates due to their hydrophilic nature. The dissolution of aluminium carbide in water can be described as follows [9]:Al₄C_3(s) + 12H₂O_(l) → 4Al(OH)_3(s) + 3CH_4(g)

It is assumed that the heterogeneous nucleation of Al₄C₃ is associated with surface defects on carbon fibres, such as exposed edges of graphite basal planes that exhibit carbon atoms with uncompensated high-energy electron bonds [8], [10]. In addition, the degree of graphitisation of the fibres determines the fibre's reactivity to nucleation of Al₄C₃ [11]. Thus, fibres with a high degree of graphitisation (containing highly oriented basal planes with few exposed edges) and a smooth surface with little topography are ideal for hindering the nucleation of carbides, due to their lack of surface defects.

In order to suppress the formation of Al₄C₃ – independently of the level of graphitisation of the reinforcing components (particles, fibres or preforms) – carbon atoms must be prevented from dissolving and their movement across the interfacial boundary has to be avoided. One approach is to coat the reinforcing component with an inert layer, which acts as a diffusion barrier between carbon and aluminium [4], [12]. A second approach considered in this study, and one much more suitable for large-scale production, is the addition of an appropriate alloying element to pure aluminium to reduce the solubility of carbon atoms in aluminium. Si is known to reduce the tendency towards aluminium carbide formation in C/Al–Si composites [13].

In the present study we used the gas pressure infiltration (GPI) method to produce interpenetrating C/Al composites. The cooling rate from the infiltration temperature is much lower in the GPI method than in indirect squeeze-casting [14]. Consequently, the probability of aluminium carbide formation is enhanced. Here we investigated the influence of different amounts of Si on the formation of aluminium carbide by carrying out infiltration runs at 750 °C. The presence of aluminium carbides was verified by optical and scanning electron microscopy, X-ray diffraction (XRD), and by a chemical method. Finally, four-point bending tests were performed to investigate the influence of aluminium carbides on the mechanical properties in the interpenetrating C/Al composites.

Section snippets

Monolithic materials

For the infiltration runs we used commercially available graphite FU2590 with an open porosity of 10 vol.%, manufactured by Schunk Kohlenstofftechnik GmbH, Germany. The thermophysical properties of this graphite preform can be found in [15]. The porous performs, with a dimension of 150 mm × 75 mm × 14 mm, were infiltrated by the gas pressure infiltration method at the Leichtmetall-Kompetenzzentrum Ranshofen (LKR), Austria. Pure aluminium (99.8 wt.%) and various Al–Si alloys were infiltrated (AlSi7,

Microstructural characterization

Fig. 1 illustrates a typical microstructure of the interpenetrating C/Al composite in question. The bright phase corresponds to aluminium, whereas the dark grey phase represents graphite and the small black spots residual porosity. At higher magnifications (see Fig. 2a), composites infiltrated with pure Al reveal the presence of needle-like phases that have grown from the C/Al interface into the aluminium phase (marked by arrows). Fig. 2a shows the surface directly after polishing. To verify

Conclusion and summary

Gas pressure infiltration at 750 °C of various Al–Si alloys into porous graphite preforms leads in all composites to the formation of aluminium carbides, independent of the Si content. Although the amount of carbides decreases with increasing silicon content, even eutectic and hypereutectic specimens exhibit distinct carbide formation. Chemical degradation of those aluminium carbides exposed to moisture occurred within a few days. The most important parameter obviously influencing the growth

Acknowledgements

The authors would like to thank the European Commission for funding part of this work under Contract No. G3RD-CT-2002-00799. Help with SEM imaging and XRD measurements from M. Siegrist and B. Zberg is also gratefully acknowledged.

References (21)

J.T. Blucher et al.
Mater. Sci. Eng. A
(2004)
A. Mortensen
Mater. Sci. Eng. A
(1991)
M.H. Vidal-Setif et al.
Mater. Sci. Eng. A: Struct. Mater. Prop. Microstruct. Process.
(1999)
J.K. Park et al.
Scr. Mater.
(1997)
M. De Sanctis et al.
Carbon
(1994)
T. Etter et al.
Mater. Sci. Eng. A
(2004)
T. Etter et al.
Carbon
(2003)
B. Revzin et al.
Compos. Sci. Technol.
(1996)
H. Prielipp et al.
Mater. Sci. Eng. A
(1995)
N.A. Travitzky
Mater. Lett.
(1998)

There are more references available in the full text version of this article.

Cited by (183)

Aluminum carbide formation in Al-graphite composites: In situ study and effects of processing variables and sintering method
2024, Materials Today Communications
The particulate-reinforced aluminum–matrix composites are interesting due to their attractive physical and mechanical properties over their monolithic counterparts, which are related to their prominent structural differences. The effect of interfacial reaction on the mechanical properties of the Al composites has been attributed to the influence of the reaction product. In this work, the formation of Al₄C₃ in Al-Gr compounds prepared by high-energy ball milling and sintered by high-frequency induction is compared with a conventional method of sintering: cold compaction and furnace sintering. The conditions related to the generation of this carbide and a precise temperature in which the initial generation of this phase occurs were determined. The different results and the in-situ characterization using HR-TEM showed the substantial reactivity of graphite in the aluminum matrix, leading to the formation of the Al₄C₃ phase within a few seconds of heating to 250 °C. The conventionally sintered samples displayed the highest number and size of Al₄C₃ precipitates. In contrast, the heated sample exhibited varied quantities and sizes of these precipitates. Notably, the high-frequency induction sintered samples contained smaller Al₄C₃ precipitates with a lower number density. Structural, microstructural, and chemical composition results of this phase formed in Al-Gr composites are also shown.
Solid-state additive manufacturing of dispersion strengthened aluminum with graphene nanoplatelets
2024, Materials Science and Engineering: A
Additive friction stir deposition (AFSD) successfully deposited graphene nanoplatelets (GNP) at concentrations of 0.0, 0.4, 0.8, and 1.1 wt% with AA6061 powders. Each concentration of GNP-AA6061 consisted of four consecutive layer-by-layer depositions on AA6061-T6 substrate. The hardness of the deposits varied from 48 Hv to 55 Hv, where a critical concentration of GNP appears to be required for a notable increase in hardness to occur (>0.8 wt%). This hardness response scaled with the tensile responses, with the highest yield and ultimate strengths belonging to the 1.1 wt% GNP of 104 ± 6 MPa and 195 ± 0.9 MPa respectively. The changes in strength are linked to grain refinement with increasing GNP content as well as a higher amount of dispersion strengthening from the GNPs within the grains. Unlike prior research on AFSD where consolidated AA6061 feedstock bars with GNPs are used, the hardness and strength is higher with this powder mixture approach.
Interfacial microstructure evolution and mechanical properties of carbon fiber reinforced Al-matrix composites fabricated by a pressureless infiltration process
2024, Materials Science and Engineering: A
In this study, unidirectional carbon fiber reinforced aluminum-matrix (CF/Al) composites were successfully fabricated by using a pressureless infiltration process to infiltrate Ni-coated CFs with Al. The evolution of the interfacial microstructure was investigated. The results showed that the Al–Ni reaction provided the main driving force for infiltration of Al melt into CF bundles by the significantly improving wettability. As the infiltration time increased from 0 min to 8 min, the infiltration behavior gradually improved with fewer defects and better fiber dispersion. Furthermore, the Al–Ni intermetallic compounds (IMCs) transformed from the large-sized primary Al₃Ni phase to fine Al₃Ni phase with eutectic structure, and were uniformly distributed around the CFs, which was beneficial for transferring the load and preventing the crack propagation. However, the harmful Al₄C₃ phase grew up at the interface. The ultimate tensile strength (UTS) of the CF/Al composites with the optimal infiltration time of 6 min was 135 ± 4 MPa, which was 121.3 % higher than that of the Al matrix.
Spark plasma sintering of graphite-chromium carbide composites: Influence of the sintering temperature and powder synthesis method
2023, Ceramics International
Carbon-metal carbide composites are a novel family of materials with potential application in heat dissipation due to the lightness and thermal-mechanical properties. Within these composites, those of graphite-chromium carbide have been still few studied. Therefore, this research focuses on both the influence of the powder preparation method (mechanical mixing (MM) and colloidal synthesis (CS)) and the spark plasma sintering (SPS) temperature (1600, 1700, 1800, 1900 and 2000 °C) in the properties of the composite graphite-7 vol. Cr. Results indicate that the composites sintered from powders processed by CS exhibit better properties, which can be explained by the better dispersion of the chromium carbide, formed during the sintering process, in the matrix of composite. Apart from the powder preparation method, sintering temperature has influence on the properties of the composite: 1900 °C is the best in the case of the route CS + SPS, while 2000 °C is the best option in the route MM + SPS. The thermal conductivity in-plane is 1.75 times greater in the CS than in the MM route, which suggests a better performance in the composite processed by colloidal route in heat dissipation applications.
Squeeze infiltration processing of lightweight smart aluminum graphite functionally graded composite for enhanced wear resistance
2023, Journal of Manufacturing Processes
Aluminum - Graphite functionally graded metal matrix composites (A356-Gr FGMMC) with 20‐60 volume percentage (vol%) of natural graphite (Gr) as reinforcement are developed by liquid metal squeeze infiltration technique. The density of A356-Gr FGMMC with 60 % Gr is reduced by 27 % (1.968 g/cm³) in particle rich region from the value of the base A356 alloy (2.68 g/cm³) making the FGMMC lighter. In comparison to monolithic A356 alloy, the coefficient of thermal expansion (CTE) of composites decreases with an increase in the volume fraction of Gr reinforcement. The CTE value is significantly reduced from 22.24 × 10⁻⁶/°C for A356 alloy to 9.62 × 10⁻⁶/°C for the composite with 60 % Gr. With the addition of Gr from 20 % to 60 %, the microhardness is found to be decreased from 74 HV to 46 HV and the compressive strength decreased from 364 MPa for the unreinforced matrix to 42 MPa for A356-Gr FGMMC with 60 % of Gr addition. Wear studies carried out on A356-Gr FGMMC using pin-on-disc tribometer shows excellent wear resistance with the addition of Gr particles compared to matrix alloy. The wear rate reduces with increasing Gr vol%, reaching a minimum at 60 % Gr. The scanning electron microscopy (SEM) analysis of worn surfaces indicate the formation of self-lubricating tribolayer which limits the interaction between matrix metal and the counter surface leading to the development of a smart composite with functionally graded properties in the particle rich region.
Influence of carbon fiber failure mode caused by TiO<inf>2</inf> coating on the high temperature tensile strength of carbon fiber reinforced 7075 Al alloy composites
2023, Journal of Materials Research and Technology
To enhance the mechanical properties of carbon fiber (CF) reinforced 7075 Al alloy material at high temperature conditions, TiO₂ coating was prepared on the surface of CF by chemical vapor deposition. The composites were prepared by hot pressing sintering and hot extrusion methods. The evolution of the compositional components of the composite interface was investigated. The density, hardness, and tensile strength of the samples were measured, and the strength/density ratio of the samples was calculated at 150 °C. The results indicate that the tensile strength of coated CF reinforced composite (535 MPa) was increased by 21.3% and 5.7% compared to the tensile strength of 7075 Al alloy (441 MPa) and uncoated CF reinforced composite (506 MPa), respectively. Furthermore, the strength/density ratio of the composite also increased with the addition of TiO₂ coating. The enhancement of coating on CF on tensile strength is attributed to the transformation of CF failure mode.

View all citing articles on Scopus

View full text

ReviewAluminium carbide formation in interpenetrating graphite/aluminium composites

Abstract

Introduction

Section snippets

Monolithic materials

Microstructural characterization

Conclusion and summary

Acknowledgements

Mater. Sci. Eng. A

Mater. Sci. Eng. A

Mater. Sci. Eng. A: Struct. Mater. Prop. Microstruct. Process.

Scr. Mater.

Carbon

Mater. Sci. Eng. A

Carbon

Compos. Sci. Technol.

Mater. Sci. Eng. A

Mater. Lett.

Review
Aluminium carbide formation in interpenetrating graphite/aluminium composites